Fiber optic monitor for railroad switch

ABSTRACT

An improved railroad switch monitoring unit of the type that determines whether a mobile rail is brought into a closed state or an open state with respect to a stationary rail. The improvement comprises a fiber Bragg grating (FBG) included in the monitoring unit that is used to determine, based on stress able change in the resonant wavelength of the FBG, whether the mobile rail and the stationary rail are closed or open.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/594,292, filed Mar. 25, 2005, hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to railway safety, and more particularly to such in railroad track switches or turnouts.

BACKGROUND ART

The railroad switch, also commonly called a “turnout,” is an important device for railroad operations. It enables trains to move from main to branch lines (or vice versa), and allows dispatchers to schedule operations. FIGS. 1 a-b (prior art) show an example of a typical railroad switch, connecting A and C in FIG. 1 a and connecting A and B in FIG. 1 b.

Railroad switches have historically been operated manually, but are now usually operated electronically by dispatchers in control rooms that can be quite far away from the actual railroad switch locations. The dispatchers thus often lack complete position information for the trains that are about to pass respective railroad switches because there is no current device being widely used to monitor for this.

Railroad switches are inherently high maintenance devices, with high wear-out rates. They require routine inspection so that proper repair or replacement can be made. Nonetheless, many incidents of failure still occur during the intervals between routine inspections. Various reasons exist for this. For example, the wear on them varies considerably, often due to factors that are unpredictable or not easily monitored. Without limitation, some of these factors include the number of trains passing and the numbers of cars in them. Other factors are the weights of the cars and the conditions of their wheels and carriages. Still other factors are the train speeds and the weather conditions.

From 1996 through 2000 approximately 200 accidents each year were attributable to problems with railroad switches. These problems were ones such as those noted, as well as others such as snow or rubbish clogging contacts (causing derailment), ballast structure changes, and wrong direction switch setting. This amounts to approximately 20% of the number of railroad accidents that occurred in each of those years.

It follows that insuring the proper operation of railroad switches is still not a well developed art, and that new and improved systems for this will provide substantial benefits in railway safety.

DISCLOSURE OF INVENTION

Accordingly, it is an object of the present invention to provide an improved system for monitoring railroad switches.

Briefly, one preferred embodiment of the present invention is an improved railroad switch monitoring unit of the type used to determine whether a mobile rail and a stationary rail are closed or open. The improvement being inclusion in the monitoring unit of a fiber Bragg grating (FBG) to determine based on changed stress in the resonant wavelength of the FBG whether the mobile and stationary rails are closed state, open, or neither.

Briefly, another preferred embodiment of the present invention is a method for determining whether a mobile rail and a stationary rail of a railroad switch are closed or open. A fiber Bragg grating (FBG) is provided and placed such that operation of the mobile rail with respect to the stationary rail stress ably effects the resonant wavelength of the FBG. The resonant wavelength of the FBG is then detected. And based on the resonant wavelength of the FBG it is determined whether the mobile and stationary rail are closed, open, or neither.

Briefly, another preferred embodiment of the present invention is an apparatus for monitoring operation of a railroad switch having a stationary rail and a mobile rail that are position able to be closed or open. A fiber Bragg grating (FBG) is provide in a mount holding it such that positioning of the mobile rail with respect to the stationary rail changes the resonant wavelength of the FBG.

These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The purposes and advantages of the present invention will be apparent from the following detailed description in conjunction with the appended figures of drawings in which:

FIGS. 1 a-b (prior art) show an example of a typical railroad switch.

FIGS. 2 a-b are cross-section views showing a switch monitoring unit in accord with the present invention, wherein FIG. 2 a shows a railroad switch in a “closed” position and FIG. 2 b shows the railroad switch in an “open” position.

FIGS. 3 a-c are a left side cross-section, a top plan, and a right side cross-section views of an exemplary switch monitoring unit, wherein FIG. 3 a particularly depicts an un-actuated condition and FIG. 3 c particularly depicts an actuated condition.

FIG. 4 is a schematic overview of an application of the switch monitoring unit with a control system.

FIG. 5 is a stylized schematic diagram depicting a large monitoring network of the switch monitoring units with local control systems and a master system.

In the various figures of the drawings, like references are used to denote like or similar elements or steps.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention is a fiber optic monitor for railroad switches. As illustrated in the various drawings herein, and particularly in the views of FIGS. 2 a-b and FIGS. 3 a-c, preferred embodiments of the invention are depicted by the general reference character 10.

In this invention, we propose to use fiber Bragg grating (FBG) sensors to monitor railway track conditions and the contact of railroad switches. The applicable physics for FBGs has been described elsewhere, including in widely available optics texts and in patent applications related to railway operations and safety by the present inventor, and therefore is not discussed in great detail herein. In brief, an FBG exhibits a resonant condition whereby it reflects light of a particular wavelength. As stress is applied to or removed from the FBG, the resonant wavelength changes. Accordingly, by providing suitable light and monitoring for changes in which wavelengths are (or are not) reflected it becomes possible to determine whether the stress on a FBG has changed.

Turning now to FIGS. 2 a-b, these are cross-section views showing a switch monitoring unit 10 in accord with the present invention. FIG. 2 a shows a railroad switch 12 in a “closed” position and FIG. 2 b shows the railroad switch 12 in an “open” position. The switch monitoring unit 10 here is shown mounted on a stationary rail 14 a, but it can alternately be mounted on a mobile rail 14 b, or anywhere that it is suitably actuated when the position of the mobile rail 14 b changes.

FIGS. 2 a-b are simplified to depict basic principles of operation. Those skilled in the art, however, will appreciate that it may be advantageous to employ two switch monitoring units 10, wherein one is used to monitor for positive positioning of the mobile rail 14 b adjacent to the stationary rail 14 a and the other is used to monitor for positive positioning of the mobile rail 14 b away from the stationary rail 14 a.

FIGS. 3 a-c are a left side cross-section view, a top plan view, and a right side cross-section view of an exemplary switch monitoring unit 10. FIG. 3 a particularly depicts the switch monitoring unit 10 in an un-actuated condition (e.g., that of FIG. 2 b) and FIG. 3 c particularly depicts the switch monitoring unit 10 in an actuated condition (e.g., that of FIG. 2 a). As can be seen, a FBG 16 embedded in optical fiber 18 here has a length “X” in FIG. 3 a that is stretched to “X+Δ” in FIG. 3 c. This produces a corresponding change in the resonant condition of the FBG 16 that can be usefully monitored.

FIG. 4 is a schematic overview of an application of the switch monitoring unit 10 with a control system 20. The control system 20 includes a light source 22, here a laser, that provides a light beam 24 having appropriate wavelength characteristics to work with the FBG 16 in the switch monitoring unit 10. The light beam 24 is carried via optical fiber 18 to the switch monitoring unit 10, where any wavelength in the light beam 24 that corresponds with the resonant condition of the FBG 16 there is reflected back, via the optical fiber 18. In its return path, however, a portion of the light beam 24 particularly passes through a beam splitter 26 to a receiver 28 (e.g., a photodetector). The receiver 28 then produces a signal, which is processed by a signal processor 30, and used by a logic unit 32 (e.g., a microprocessor) to make a determination whether the railroad switch 12 is open or closed and to communicate that information as appropriate.

Various levels of sophistication can be utilized by the control system 20. For example, without limitation, the light source 22 can produce the light beam 24 with λ₃=λ_(O), wherein λ_(O) is the resonant wavelength of the FBG 16 when the switch monitoring unit 10 is not actuated and λ_(O+Δ) is the resonant wavelength of the FBG 16 when the switch monitoring unit 10 is actuated. The receiver 28 will then receive most of the light beam 24 (λ₃) as long as the switch monitoring unit 10 is not actuated (i.e., the railroad switch 12 is presumably “open”). Conversely, the light source 22 can be set to produce the light beam 24 with λ₇=λ_(O+Δ), and the receiver 28 will then receive most of the light beam 24 (λ₇) only when the switch monitoring unit 10 is actuated (i.e., the railroad switch 12 is presumably “closed”).

Such “binary” embodiments can serve in many applications. In other applications, however, it may be desirable to have more information. The light source 22 used then can be one able to produce the light beam 24 with a broad band of wavelengths, say with λ₁₋₉. The receiver 28 used here can then be one that monitors for this range of wavelengths. If λ₃ is received most strongly, the control system 20 can report that the railroad switch 12 is open. If λ₇ is received most strongly, the control system 20 can report that the railroad switch 12 is closed. If any of λ_(1, 2, 4, 5, 6, 8, 9) is received most strongly, or if no reflected wavelength is detected at all, the control system 20 can report that inspection is advisable and that some manner of repair or replacement may be needed. This can be termed a pseudo analog approach, wherein a reflected wavelength other than λ₃ (open) or λ₇ (closed) has informative value.

Since the FBG 16 can detect very small changes, even as little as a few microns of physical movement, phenomena such as clogging of the railroad switch 12 due to snow or rubbish, a malfunction in the closing of the railroad switch 12, or abrupt changes in the civil structure adjacent to the railroad switch 12, etc., can all easily be detected and appropriate information can be reported to a dispatcher or other appropriate authorities in real time.

The present invention can also provide a number of optional, subtle benefits. The distance that the light beam 24 can reliably travel through the optical fiber 18 can be considerable, potentially hundreds of kilometers without amplification. The switch monitoring units 10 can also be connected into parallel or serial (“Daisy chain”) configurations with the optical fiber 18. Serial arrangements are straightforward. In parallel arrangements, demultiplexing the various wavelengths in the reflected light beam 24 permits determining the state of the railroad switch 12 at each switch monitoring unit 10.

FIG. 5 is a stylized schematic diagram depicting a large monitoring network 40 of switch monitoring units 10, local control systems 20, and a master system 42. The switch monitoring units 10 inherently have resonant wavelengths in their respective states of interest, and these are shown in FIG. 5. The control systems 20 and the master system 42 communicate via communications links 44.

A topmost control system 20, 20 a in FIG. 5 serially connects to four switch monitoring units 10 arranged in two pairs. For example, one pair of the switch monitoring units 10 could be employed at a first railroad switch, with one configured to reflect λ₁ when it is affirmatively stressed by the switch being closed and the other configured to reflect λ₂ when it is not stressed by the switch being open. The second pair of switch monitoring units 10, those using λ₃ and λ₄, could then be similarly employed at a second railroad switch 25 kilometers away. If the control system 20, 20 a here “sees” λ₁ and not λ₂ reflected back, this indicates that the first (closest) railroad switch is closed. Similarly, if the control system 20, 20 a here sees λ₃ and not λ₄ reflected back, this indicates that the first (furthest away) railroad switch is closed. However, if the control system 20, 20 a sees both λ₁ and λ₂, or neither of these, or both λ₃ and λ₄, or neither of these, this indicates that something is awry.

A second topmost control system 20, 20 b in FIG. 5 serially connects to only a single switch monitoring unit 10, but it is one quite distant from the control system 20, 20 b here. As discussed above, the use of optical fiber 18 (FIG. 4) to connect the switch monitoring units 10 and the control systems 20 can permit quite economical and robust use of the present invention even across quite large distances.

A third topmost (second bottom most) control system 20, 20 c in FIG. 5 connects to two switch monitoring units 10. One of these is a stressed unit 10 a that is stressed by the mechanical action of a railroad switch being operated and the other is an unstressed unit 10 b that is not mechanically stressed in this manner. As described in more detail below, the control system 20, 20 c here can perform a differential comparison of the respective wavelengths reflected back from these switch monitoring units 10 a, 10 b to obtain a higher degree of confidence whether or not the mechanical action of a railroad switch is what is actually being observed. The control system 20, 20 c and the switch monitoring units 10 a, 10 b here are all in relatively close proximity, although there is no particular need for this to be the case.

And a bottom most control system 20, 20 d in FIG. 5 connects to many switch monitoring units 10 configured in both serial and parallel arrangements, and located at varying distances from the control system 20, 20 d and from each other.

The communications links 44 between the control systems 20 and the master system 42 can be of various types and in various arrangements, as motivated by the typical factors for communicating similar distances in similar environments. For example, without limitation, the control systems 20 a, 20 b in FIG. 5 communicate with the master system 42 via conventional telephone lines 44 a (or via dedicated phone lines, or via cellular telephone). The control system 20 c does not communicate directly with the master system 42. Instead the control system 20 b and the control system 20 c intercommunicate directly via an Ethernet local area network (Ethernet LAN 44 b), and the control system 20 b “forwards” message traffic between the control system 20 c and the master system 42. The control system 20 d in FIG. 5 communicates with the master system 42 via the Internet 44 c. In this latter exemplary instance, the control system 20 d itself may handle all matters related to railroad switch operation locally, yet still communicate onward with the master system 42 so that more detailed analysis or analysis in combination with information from the other control systems 20 can also be performed.

As a device, a FBG is generally subject to temperature as well as stress. On first consideration, this may seem a disadvantage. Where that is the case, however, it can be dealt with. For example, the present inventor's company, Fibera, Inc. of Santa Clara, Calif. is a provider of a thermal FBGs. Alternately, the control system 20 can include a compensating capability (e.g., a temperature measurement system under control of the logic unit 32). Still alternately, a second FBG 16 can be provided proximate to the first one, but mounted such that it is not stressed (see e.g., switch monitoring units 10 a, 10 b in FIG. 5). Differential processing of the reflected light from the two FBGs 16 will then be a very accurate indication of the stress on the first FBG 16 that is actually attributable to operation of the railroad switch 12.

On deeper consideration, however, having the FBG 16 subject to temperature as well as stress can be turned into an advantage. With relatively little added, the control system 20 can report on the temperature at one or more railroad switches 12. Thus, personnel can be made aware if the temperature on a particular stretch of distant railway line is so hot that the rails there may have shifted or started to buckle. A railway dispatcher can then instruct train engineers to proceed at a slower, safer speed on that localized stretch and a railway traffic clerk can adjust system-wide scheduling accordingly. Alternately, personnel and apparatus can be made aware if the temperature on a particular stretch is approaching or already below freezing. Ice and snow are notorious for causing railroad switch problems. In many parts of the world, railroad switches have to be provided with heaters to melt away ice and snow. The present invention can therefore be embodied to better inform personnel when ice or snow is a valid concern, or to automatically engage heaters when and only to the actual extent needed.

Traditional, electrically monitored track switches are also subject to another powerful force of nature, lightning. The inherent conductive nature of railway rails and the typically long paths that electrical wiring to and from track switches must travel puts conventional electrical track switches and their control systems at great risk. A lightning strike some distance up or down a railway line can thus disable a track switch. Lightning strikes anywhere along the electrical wiring path can also induce electrical noise into the system that triggers false reports or even burns out switch or control system components.

In contrast, the present invention is substantially non-electrical. Aside from the control system 20, which can be shielded easily, the present invention is simply not effected by lightning unless it strikes so directly and powerfully that heat or explosive force physically damages components. As for induced electrical noise, the FBG 16 and the optical fiber 18 of the present invention are immune to it.

Since the FBG 16 in each switch monitoring unit 10 can have a unique resonant wavelength, the traffic at each of multiple railroad switches 12 can be monitored distinctly. When a train passes by or is at rest at the location of a railroad switch 12, the rails are temporarily deformed by the weight of the train. By appropriate attachment of a switch monitoring unit 10, this deformation produces an instantaneous stretch or relaxation to the FBG 16 that is proportional to the weight of the train. When multiple switch monitoring units 10 (or the present inventive switch monitoring units 10 together with other FBG-based railway systems by the present inventor) are used along a railway track, the direction and the speed of train movement can be determined. With two units, determining direction can be as simple as seeing which switch monitoring unit 10 is actuated first. Since the position of each switch monitoring unit 10 is fixed, measuring the amount of time for a train to travel from one to the other permits speed calculation. Further, if three or more switch monitoring unit 10 are mounted at known positions, the acceleration of a train can also be calculated. All of this additional information can permit railway personnel and other appropriate authorities to insure more efficient and safe railroad operations.

While various embodiments have been described above, it should be understood that they have been presented by way of example only, and that the breadth and scope of the invention should not be limited by any of the above described exemplary embodiments, but should instead be defined only in accordance with the following claims and their equivalents. 

1. An improved railroad switch monitoring unit of the type that determines whether a mobile rail is brought into a closed state or an open state with respect to a stationary rail, the improvement comprising: a fiber Bragg grating (FBG) included in the monitoring unit to determine based on stress able change in the resonant wavelength of said FBG whether the mobile rail and the stationary rail are in any of the closed state, the open state, or neither.
 2. A method for determining whether a mobile rail and a stationary rail of a railroad switch are in a closed state or an open state, the method comprising: providing a fiber Bragg grating (FBG) placed such that operation of the mobile rail with respect to the stationary rail stress ably effects the resonant wavelength of said FBG; detecting the resonant wavelength of said FBG; and determining based on the resonant wavelength of said FBG whether the mobile rail and the stationary rail are in the closed state, the open state, or neither.
 3. The method of claim 2, wherein said step of detecting includes: defining a closed wavelength to be the resonant wavelength of said FBG when the mobile rail and the stationary rail are in the closed state; defining an open wavelength to be the resonant wavelength of said FBG when the mobile rail and the stationary rail are in the open state; directing a light beam including at least one of said closed wavelength and said open wavelength to said FBG via an optical fiber; receiving any reflected portion of said light beam back from said FBG via said optical fiber; and sensing whether said any reflected portion includes any of said closed wavelength and said open wavelength.
 4. An apparatus for monitoring operation of a railroad switch having a stationary rail and a mobile rail position able into a closed state or an open state with respect to the stationary rail, the apparatus comprising: a fiber Bragg grating (FBG); and a mount holding said FBG such that positioning of the mobile rail with respect to the stationary rail changes the resonant wavelength of said FBG.
 5. The apparatus of claim 4 wherein a closed wavelength is defined to be the resonant wavelength of said FBG when the mobile rail and the stationary rail are in the closed state and an open wavelength is defined to be the resonant wavelength of said FBG when the mobile rail and the stationary rail are in the open state, and wherein the apparatus is comprised within a monitoring system including: a light source to produce a first light beam including at least one of said closed wavelength and said open wavelength; a light receiver to receive a second light beam and sense whether it includes any of said closed wavelength and said open wavelength; and an optical fiber to direct said first light beam from said light source to said FBG and to return any said second light beam reflected from said FBG to said light receiver.
 6. The apparatus of claim 4, wherein said light source includes a laser.
 7. The apparatus of claim 6, wherein said laser concurrently produces a range of light wavelengths that encompass said closed wavelength and said open wavelength.
 8. The apparatus of claim 6, wherein said laser tune ably produces a specific light wavelength within a range of light wavelengths that encompass said closed wavelength and said open wavelength. 